This invention relates to serial impact printers and, more particularly, to serial impact printers employing rotatable character arrays such as a print wheel or daisy.
A print wheel of the daisy type, as shown in U.S. Pat. No. 3,949,853--Lahr et al, comprises a central hub portion which is removably coupled to the drive mechanism for the print wheel and a plurality of petals or radially-extending spokes which carry the various character elements at the radial extremities thereof in circumferentially spaced positions about the print wheel. Print wheels or daisies of this type may be utilized in a variety of applications. For example, print wheels may be used in serial printers such as those manufactured by Qume and Diablo, which are associated with communications terminals, computer output devices and other printing applications in the data processing field. In addition, such print wheels may be and are utilized in typewriters including equipment manufactured by Xerox Corp.
One important consideration in mounting a print wheel of the daisy-type is the manner in which the print wheel may be removed from the rotary drive mechanism. Removability and/or replacement of the print wheels is particularly important since the print wheels are subjected to a substantial battering force by the hammer. In addition, it is desirable, particularly in typewriter applications, to permit removability or replacement of the print wheel so as to allow for selection of a particular style of type by merely changing print wheels.
Replacement or removability of print wheels has been achieved in the Xerox typewriters which employ daisies by hinging the print wheel carriage so as to allow the print wheel and drive to be moved upwardly and away from the opposing platen. Once moved to this position, the print wheel may be extracted by pulling the print wheel from the end of the drive shaft since the platen is no longer in a position of interference with respect to that drive shaft. See also U.S. Pat. No. 3,707,214--Ponzano. Replacement of the daisy has also been achieved by hinging the printing hammer as shown in U.S. Pat. No. 3,651,916--Bacchi, so as to allow the daisy to be removed from the drive shaft.
In Ser. No. 809,923, filed June 24, 1977 by Dan W. Mathias and Richard E. Thornton, which is assigned to the assignee of the present invention, it is disclosed that it is desirable to form a daisy type character array as a unitary structure with the rotor of a high performance rotary stepper motor because such a structure reduces the mass of the combination character array and character array drive unit. This reduction in mass is advantageous in printers having a daisy or print wheel adapted to mount on a movable carriage because the smaller the overall mass of the carriage and its contents, the less energy is required to accelerate and decelerate it. In the daisy design disclosed by Mathias and Thornton, the combination character element/rotor element is mounted within the axial air gap situated between an excitable stator segment and a non-excitable stator segment. In the printer disclosed by Mathias and Thornton, the problem of removing and replacing the print wheel or daisy is aggravated due to the fact that the axial air gap is a very confined area. Accordingly, Mathias/Thornton disclosed a two-part shaft, the parts being adapted to mate end to end in axial alignment with one another to clamp the daisy character array therebetween. In mounting the character element using this arrangement, the daisy is first positioned within the air gap and a chamfered surface on the end of one of the two shaft parts axially guides the daisy into the proper position prior to its being clamped in place.
One problem associated with this arrangement has been that it is difficult for the operator of the printer to accurately center the daisy such that the chamfered surface may be an effective guide. Thus, it has been found that the daisy character element has been clamped to the shaft while not being properly aligned.
Another problem associated with this design has been that the two part shaft has not provided for sufficient rigidity of the daisy character element. Since the exact location of the daisy is critical to the printer's operation, a lack of rigidity of the shaft may make it difficult to maintain a fixed position of the character element which is fastened thereto.
A still further disadvantage has been that it has been difficult to remove the daisy after it has been positioned within the axial air gap since when the two part shaft has been separated, the daisy tends to fall through the air gap of the stepper motor to the bottom of the carriage.
It is an object of the present invention to provide a means for quickly mounting a daisy type character element to an impact printer.
It is a further object of the present invention to provide for ease in removability and replacement of a rotatable character array.
It is still a further object of the present invention to provide a means for mounting and locking a rotatable character array within the air gap of a rotary stepper motor.
It is a still further object of the present invention to provide a means for mounting and locking a rotatable character array in a fixed and unvarying position.
It is a still further object of the present invention to provide a means for quickly and easily dismounting a rotatable character array from an impact printer.